A thin CRT display is a type of flat panel display which uses a matrix of cold cathodes to emit electrons towards an anode faceplate coated with phosphors. The most promising type of thin CRT displays use Spindt field emission cathodes, and they are often called Field Emission Displays (FED). Another promising type of thin CRT displays use Surface Conducting Electron (SCE) cathodes developed by Canon. And other kinds of cold cathode which can be used to construct thin CRT displays include MIS cathodes developed by Pioneer Electric Corp. (which is also called High Efficiency Electron-Emission Device, or Heed) , Silicon avalanche cathodes developed by Philip, diamond cathodes developed by SI Diamond, MIM cathodes, pn junction cathodes and Schoftky junction cathodes.
Thin CRT displays have the potential to provide image qualities comparable to conventional CRT displays. But, because the light intensity of each pixel is determined by the electron emission characteristics of one or more cold cathodes behind the phosphors segment of that pixel, it is difficult to make thin CRT displays with uniform display intensity. The variations of the display intensity is due to the variations of the electron emission characteristics of all the cathodes. The variations of the electron emission characteristics are inevitable, because large numbers of cathodes have to be manufactured over a very large area. It is important to improve the display uniformity, if one want to make thin CRT displays with large number of gray levels, such as 256 levels for each color.
There have been many attempts to improve the display uniformity of thin CRT displays. Some of the methods, such as those described by U.S. Pat. No. 5,637,023 and No. 5,610,471 and the references cited therein, try to use better manufacture techniques to improve uniformity of all cold cathodes. And some of the methods, such as those described by U.S. Pat. No. 5,157,309 and No. 5,581,159, try to use better driver electronic designs to improve the electron emission uniformity of all the cathodes. And there is still some other methods, such as U.S. Pat. No. 5,514,937, which use memory element associated with each electronic driver to compensate the variations among different cathodes. All these methods only provide limited success, and some of these methods are complicated and expansive to implement.
In this document, the applicant present a new method, which the applicant claims to solve the uniformity problem of thin CRT displays once for all. The new method provides almost perfectly uniform display properties for thin CRT displays regardless the inevitable variations of each cathode. The new method disclosed in this document is performed in three steps: First, the emission characteristics of every cathode in the display is measured. Second, the correct driving parameters for each cathode--used as calibration parameters directly--are calculated and stored in a calibration memory as a complete look-up table, or the calibration parameters for each cathode are calculated and stored in a calibration memory as a partial look-up table. Third, using the complete look-up tables or using partial look-up tables in combination with additional calculation, the correct driving parameter for any cathode with any luminosity level can be obtained, and the correct driving parameters are used to drive the thin CRT display. For the first step described above, the emission characteristics of all cathodes can be measured by a current detector connected to the anode, or can be measured in a dark chamber by turning on one cathode at a time. For the second step described above, linear approximation or other higher order approximation can be used. For the third step, there are two general embodiments: (1) with embodiment one, all the calculated correct driving parameters are stored in a video memory and driver electronics use these calculated correct driving parameters in the video memory to drive the display; (2) with embodiment two, the desired light intensities are stored in a video memory without any compensation, and using the complete look-up tables or using partial look-up tables in combination with additional calculation, the driver electronics calculate the correct driving parameters by fetching the light intensities from the video memory and use these calculated correct driving parameters to drive the display directly. For both embodiments mentioned above, when partial look-up tables are used, additional calculations are needed to obtain the correct driving parameters, and these calculations can be performed by the main microprocessor or a dedicated display processor.